1. Field
The present invention relates generally to a method and a system for multi-dimensional visualization of the spinal column, and more specifically to techniques for 3D visualization of the spinal column comprising vertebral size, position, orientation and rotation and their utilization for description, characterization and quantitative parametric analysis of spinal deformities in frontal, sagittal and horizontal plane.
2. Background
Scoliosis is the most prevalent three-dimensional (3D) spinal deformity affecting about 1% of adolescent population. Diagnosis and classification of scoliotic deformities is almost exclusively based upon frontal and lateral X-ray images. Current classification of adolescent scoliosis has been proposed to be comprehensive and all-inclusive for every curve types but in addition to classifying frontal spinal deviations it only considers sagittal spinal alignment, and ignores axial vertebral rotation [1] that is thought to be an inherent characteristics of scoliotic 3D deformities presented in horizontal plane. The demand for an accurate evaluation of vertebral rotation in scoliosis is hardly new. Biplanar X-ray images provide inadequate quantitative or qualitative information on the anatomical landmarks needed to determine the axial rotation [6,21]. Several measurement methods have been published [2-5], all based on assessment of the relative positions of various posterior vertebral elements. Perdriolle torsiometry [3,4] is currently the most accepted measurement method in clinical practice, but its reproducibility is very limited and cannot be quantified precisely [6,7].
Horizontal plane deviations of the spine are most accurately assessable by computed tomography, but routine use of this diagnostic method is limited due to its relatively high cost and prohibitively high radiation dose [8,9]. Expert opinion is divided on the veracity and reproducibility of CT scans for such measurements [10,11].
The latest classification proposal introduced the concept of the plane of maximum curvature (PMC) and visualization of the PMC through the daVinci representation, which is thought to make the 3D evaluation of scoliosis readily available for routine clinical practice [13].
U.S. Pat. No. 5,582,186 discloses measurement principles and bar plot representation of measured values of the absolute axial rotation and relative intervertebral rotation of individual vertebrae. They perform the measurement of vertebra rotation based on a formerly published indirect method determining the center of the body of vertebra and calculating the relative position of this center point inside the contour lines of the body of vertebra. The method itself is indirect, because the rotation in the horizontal plane is calculated based on anatomical reference points visible in the frontal plane where the accuracy of determination and reproducibility is inadequate, thus reliability of the presented method is low. In addition to vertebral rotation, other three-dimensional properties of the vertebrae (e.g. 3D-position, frontal and sagittal rotation) remain undetermined; the method is not capable for proper 3D characterization of the vertebral column.
US20070073194 describes a method dedicated exclusively for measuring the axial rotation of vertebrae. This solution is based on the principle described by Pedriolle et al. (also cited in our PPA reference list). The horizontal symmetry axis of vertebrae is given by a line defined by the center point of the vertebral body and the end of spinous process. The extent of rotation is estimated by a relative positional change of the ovoid patterns representing the frontal projection of vertebral pedicles. Summarized, this method also determines the extent of axial rotation indirectly. The accuracy and reproducibility has been found to be weak and reliability is considered to be low. In addition to vertebral rotation, other three-dimensional properties of the vertebrae (e.g. 3D-position, frontal and sagittal rotation) remain undetermined; the method is not capable for proper 3D characterization of the vertebral column.
The method known from US20090202122 has been elaborated for determining the centre line of the vertebral column (which surrounds the spinal chord) in the frontal and mainly in the sagittal plane. On axial (or sagittal) tomographic images (e.g. computed tomography) the valid center points for every slice are determined with the help of the posterior vertebral arches and the frontal and rear endpoints of the vertebral foramen; from the series of centre points derived from consecutive slices the position and direction can be represented. Some common feature with the basis of the theory of vertebra vector might be discovered because the origin of the vertebra vector is positioned around the area of the vertebral foramen but is not identical with the centre point of those. Considering that it only represents a spatial alignment of series of points in form of a simple line; it is only capable of defining a three-dimensional position of series of points. It contains no information on the body of vertebrae themselves which lie in front of the vertebral foramen and is unable to provide spatial information and measurement data on rotation and size of those.
US20090226055 describes a method using the fundamental principle of three-dimensional characterization and classification of vertebral column by presenting the plane of maximum curvature, PMC with daVinci representation for scoliotic vertebrae, which is currently being advocated by Scoliosis Research Society as a superior solution to the problems of 3D visualization and characterization of the spine. PMC is a derivative plane defined by 3 centroids of the vertebral bodies determining the scoliotic curve and its horizontal projection is displayed in a Da Vinci graph to be characterized numerically. The very aim for introduction of this method was to provide an assessment for the horizontal plane spinal deviations, namely, axial vertebral rotation. This new method has been available as a new recommendation for two years, but it did not reach a great success with clinicians because it may be too much as an abstraction and too difficult to be comprehended and a little complicated to be presented based on stereographic X-ray images. It is an indirect and incomplete method, is bound to the determination of an invisible, hardly imaginable and complicated 3D plane which falls outside of the vertebral column. For a truly complete 3D characterization of the spinal column, it requires additional data of frontal and sagittal plane spine deviations determined by independent methods. Its relation to the known measurement methods has not been proven yet.
A new low-dose digital radioimaging device based on a Nobel Prize winning X-ray detection technology creates spatially calibrated, simultaneously captured frontal and lateral X-ray images in a standing position of the whole body, available and approved for clinical practice [14,15,16,17]. A special semiautomatic 3D reconstruction software, based on these biplanar calibrated radiographs generates accurate and realistic surface 3D model of thoracic and lumbar vertebrae and the pelvis, complemented with 3D parametric values of frontal and sagittal spinal curves, vertebral orientation and rotation in all 3 planes and sagittal pelvic parameters [18,19]. From representations of planar projections of surface 3D reconstructions, visualization of the spinal geometry in horizontal view has become a routine daily task in scoliosis surgery.
Nevertheless, precise 3D reconstructions from current radiodiagnostic devices provide a very complex visual information that contains way too much data to be computed and extracted, in order to simply characterize and numerically describe spinal deformations, especially in the horizontal plane.
Due to the lack of a definitive and reproducible measurement method in horizontal plane and a need for a simplified yet all-inclusive presentation of the spinal column based on 3D reconstruction images of current radiodiagnostic methods, a new method and system of vertebra vectors is introduced that is capable of the complete visualization, characterization and numerical description of spinal deformities in all 3 planes while preserving conventional methods for the measurement of frontal and sagittal plane curvature of the spine.